Compressors, turbines, other forms of commercial equipment frequently generate and utilize fluids having a high temperature and/or pressure. For example, a typical gas turbine includes a compressor at the front, one or more combustors radially disposed about the middle, and a turbine at the rear. Ambient air enters the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to increase the pressure of the working fluid and bring it to a highly energized state. The compressed working fluid flows to one or more combustors which mix fuel with the compressed working fluid and ignite the mixture to produce combustion gases having a high temperature and pressure. The combustion gases exit the combustors and flow along a hot gas path through the turbine. One or more casing(s) generally surround the turbine to contain and direct the combustion gases through alternating stages of fixed nozzles and rotating buckets. The rotating buckets may be attached to a rotor so that expansion of the combustion gases flowing through the turbine stages causes the buckets, and thus the rotor, to rotate to produce work.
During testing, maintenance, and operations, it is often desirable or necessary to monitor or measure conditions or components inside the commercial equipment. For example, an optical probe may be used to monitor vibrations, clearances, oscillations, or other parameters of the rotating blades in the compressor or the rotating buckets in the turbine. Similarly, a temperature sensor, pressure sensor, or other instrument may be inserted to monitor temperatures, pressures, and other internal parameters of the working fluid in the compressor or the hot gas path in the turbine. In each case, the particular instrument must generally be positioned at a precise location so that it is close enough to the component being monitored without contacting, rubbing against, or otherwise interfering with the rotating components.
In many cases, the instrument must pass through openings in an inner and/or outer casing to reach the component being monitored. Inasmuch as the inner and/or outer casings may expand at different rates and by different amounts, the size of the openings through the casings must be larger than the instrument so that radial and/or axial expansion of the casings does not cause the casings to interfere with the position of the instrument. Specifically, as the casings expand or contract, contact between the casings and the instrument may shift the position of the instrument, affecting the accuracy of the instrument and/or causing contact between the instrument and rotating components. However, increasing the size of the openings to accommodate expansion and contraction of the casings creates additional space between the openings and the instrument. The additional space between the openings and the instrument may allow excessive amounts of working fluid or combustion gases to leak past the inner casing, causing excessive heat and/or damage to components outside of the inner casing. Therefore, a system and method that allows for accurate placement of the instrument through one or more casings without allowing excessive amounts of fluid or gases to leak through the casings would be useful.